Electron discharge device



May 23, 1939.- J. L. H. JO'NKER ET AL 2,159,765

I ELECTRON DISCHARGE DEVICE Filed May 2'7, 1938 E: b v.

IIII 11111 11 INVENTORS JOHAN L.H. JONKER BY BERN DUS O.M GALL ATTORNEY.

Patented May 23, 1939 UNITED STATES PATENT OFFICE s f 2,159,765ELEGTRONI DISCHARGE. DEVICE.

2 Claims. (Ci. est-27.5)

This inventionrelates to a multi-grid electron .discharge tube having aplurality of control grids andxparticularly suitablecas a so-calledmixer jlfltube in superheterodyne circuits. The invention *5Siurthermore relates to such a tube and to a circuit in which such atube can be used.

{In theconventional tubes of thistype ordinarily between a cathode andan anodela number of grid-shaped electrodes are arranged of which 10.two are employed as control grids,'one on which i the received signalvoltage is impressed and the other on which the local oscillator voltageis impressed. The two control grids are disposed ordinarily directlybehind one another which involves j lthe, disadvantage that these gridshave a high I capacity relative to each other. a

i To reduce this capacity in tubes having a pair of control grids suchas for instance the mixer tubes, and octodes, at least one grid servingas a 20 screen grid and having a positive potential is 1 positionedbetween the control grids. In this case the second control grid usuallydoes not control f directly the electrons leaving the cathode butcontrols a space charge, a s-ca1ledvirtual cathi ld olde, which formsbetween the positive screen electrode and the second control grid.Though with this arrangement favorable results can generally beobtained, in certain cases suchtubes have the disadvantage that dueto'the space I l charge which is influenced by the second control grid,a current distribution appears which among other things causes aconsiderable increase of the rustling noises developed in the tube.

[ j Applicants have found that this disadvantage 35 can be overcome whenemploying an arrangement and an electron discharge tube in accordancewith the present invention. According to our invention a tube having twocontrol grids has positioned betweenthe grids instead of a screen elec40 trode, at a positive potential, screens between a parts of thecontrol grids, these screens being connected to a point having zeropotential or a fixed negative potential.

{Since the control is exerted upon two successive grids so that bothcontrol'grids influence 50 posed between parts of the grids and aresuitably connected to a point having zero potential such as {forinstance the cathode. These screens are then usually arranged betweenplaces of the control grids at which very few. electrons appear, forinstance in the case of an oval cathode at places opposite the narrowsides, or in the region of the grid side rods.

In order further to reduce the noise of a discharge tube in accordancewith the present invention, in accordance with a specific mode of con.struction the grid situated at the anode side of the second control gridand which may serve as a screen grid is so designed that the effectiveparts of this grid are aligned with the effective parts of the secondcontrol grid. In other words, the

turns of the second control grid and the screen grid are aligned. Inorder to reduce the screen grid current further it is possible to alignalso 'some of all effective parts of control grid I. with those of thesecond control and the screen grids. l6 s A discharge tube and anarrangement according to the present invention are especially wellsuited for use in mixer circuits of an intermediate frequencysuperheterodyne receiving circuit.

In a discharge tube according to the invention and employed as mixertube the first grid can be used as an input control grid, and the secondcontrol grid as an oscillator control grid, or vice versa, whereby theoscillations of the local oscillator may be produced by means of aseparate'triode. In accordance with a certain mode of construction,according to the present invention, the mixer system and the triode mayhowever also be combined to form a single tube. Such a tube contains inthis case an indirectly heated cathode surrounded along a portion of itslength by a single grid, and an anode, while there is placed aboutanother portion of the length of the cathode an electrode system asdescribed above and comprising two control grids with interposed screenmain- 3 tained at zero potential or negative potential, a screen gridand an anode, whereby in addition an absorption or suppressor grid maybe arranged between thescreen grid and the anode.

The novel features which we believe to be char- 40 acteristic of ourinvention are set forth with particularity in the appended claims, butthe invention itself will best be understood by reference to thefollowing description taken in connection with the accompanying drawingin which Figure 1 number of grid-shaped electrodes 2, 3, 4 and 5surrounding and coaxial with said cathode and which are usedrespectively in a discharge tube, and an arrangement according to thepresent invention, as first control grid, second control grid, screengrid andabsorption or suppressor grid. Small screen plates 6, which maybe of sheet metal, are arranged between the grids 2 and 3 and at places,i. e. between parts at which but few electrons appear, in comparisonwith the other parts of the grids. The various grids are fastened tosupporting rods 1 which all lie in the same plane to provide a fielddistribution as favorable as possible. Finally, an anode 8 is placedabout the said grids. The electrode assembly is placed within anevacuated envelope 8'.

Figure 2 shows a circuit in accordance with the present invention. Inthis circuit two tubes 9 and ID are shown of which the first one isemployed as triode oscillator, containing a cathode I I, a grid [2 andan anode I3, while the second tube represents a mixer tube in accordancewith the invention, containing a cathode I, two control grids 2 and 3, ascreen grid 4, an absorption grid 5 con nected to the cathode, then ananode 8, and two small screen plates 6 likewise connected to thecathode. In the drawing there is shown furthermore an input circuit 2 I,an output circuit 22, and

an oscillatory circuit 23 whereby the oscillations produced in the tube9 are impressed upon the grid. l6 of the tube ID to provide a voltage ofintermediate frequency in output 22.

. While we have indicated .the preferred embodiments of our invention ofwhich we are now aware and have also indicated only one specificapplication for which our invention may be employed, it will be apparentthat our invention is by no means limited-to the exact forms illustratedor the use indicated, but that many variations may be made rods lying ina common plane, and a pair of shielding members positioned between thecontrol grids and lying adjacent said side rods and providing openingson opposite-sides of said cathode through which electrons from saidcathode may travel to said anode.

2. An electron discharge device having a straight thermionic cathode andan anode surrounding said straight thermionic cathode, a pair of controlgrids surrounding and coaxial with said cathode and positioned betweenthe cathode and anode, and a screen grid surrounding said control grids,each of said grids being provided with a pair of side rods,said siderods lying in a common plane, and a pair of V-shaped shielding memberspositioned between the control grids and lying adjacent said side rodsand providing openings on opposite sides of said cathode through whichelectrons from said cathode may travel to said anode, said shieldsconnected to cathode.

JOHAN LODEWIJK HENDRIK JONKER. BERNARDUS OCTAVIANUS MARIA GALL.

